1. Field of the Invention
This invention relates to a diaphragm valve, and more particularly to a diaphragm valve having a back-up seal which prevents both the leakage of fluid and the expulsion of fractured valve components out of the valve.
2. Description of the Prior Art
In valves controlling the flow of fluids, particularly at high pressures, it is necessary to provide suitable sealing means which prevent the leakage of fluid out of the valve and furthermore prevent the expulsion or blow-out of internal valve components out of the valve which would otherwise present a risk of property damage and injury to operating personnel. U.S. Pat. Nos. 2,061,028; 2,144,754; 2,647,538; 2,925,987; 2,983,480; 3,084,901 and 3,523,551 illustrate and describe valves having sealing arrangements, such as diaphragms, bellows, O-rings, packing materials and other suitable sealing devices to prevent leakage around the valve stem and through the open end portion of the valve chamber.
U.S. Pat. No. 2,647,538 discloses a packing arrangement positioned between a retainer sleeve member and a stem member provided within a chamber of a valve for controlling the flow of steam or hot water. The packing is held in place by the packing retainer and is compressed by a ring. The ring is urged downwardly by a coil spring and the compression of the spring is adjustable by a packing nut threaded into the upper portion of the retaining sleeve. The packing functions to prevent the leakage of steam from the valve chamber along the valve stem. The packing arrangement is contained entirely within the body of the valve. To vary the compressive forces applied by the spring to the packing, the entire valve must be disassembled and the packing nut adjusted by a suitable tool to increase or decrease the compressive forces exerted by the spring on the packing.
U.S. Pat. No. 3,237,917 provides rings of packing material surrounding the valve stem within an annular recess forming part of the valve chamber. The packing is supported against the valve chamber by annular ring support members and is compressed by a follower upon which a gland bears. The gland is suitably engaged to the body of the valve within the valve chamber. The gland exerts a predetermined amount of compression upon the follower which, in turn, is transmitted to the packing. A lock nut threadably engaged within the valve chamber to the gland maintains the gland immovable within the chamber and fixed relative to the follower. Thus the gland is maintained immovable with the valve chamber. Consequently, the compressive forces applied by the gland to the follower and transmitted to the packing ring cannot be varied.
U.S. Pat. No. 3,523,551 illustrates and describes a faucet capped by a stuff nut provided with a cylindrical recess surrounding the valve stem and adapted to receive a sealing assemblage. The sealing assemblage includes an O-ring seal confined within the recess between a bearing member and a disc. A compression spring acting through the bearing member exerts a downwardly directed force against the O-ring seal. The compressive force of the spring transmitted to the O-ring seal remains a constant predetermined valve and is not capable of adjustment externally of the faucet chamber.
There is need for a diaphragm type valve provided with a sealing arrangement to prevent the leakage of fluid from the valve chamber and, in turn, prevent the expulsion of broken valve components out of the valve. Furthermore, there is need for a diaphragm valve having a back-up seal contained internally within the valve by the application of compressive forces thereto. The compressive forces applied internally within the valve chamber must be adjustable externally of the valve to permit the application of forces at selected levels as needed to resist the fluid pressure in the pipeline and wear upon the sealing members.